chapter 2 the chemical basis of life. thomas eisner pioneered _______ __________ __________ –the...
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CHAPTER 2The Chemical Basis of Life
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Thomas Eisner pioneered _______
__________– the study of the
chemical language of nature
He studies how insects communicate via chemical messages
Thomas Eisner and the Chemical Language of Nature
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Water in three different states: 5 States of matter
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Everything an organism is and does depends on chemistry
Chemistry is in turn dependent on the arrangement of atoms in molecules
In order to understand the whole, biologists study the parts (reductionism)
The emergence of biological function starts at the chemical
level
ATOMS AND MOLECULES
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A _________________
A. Molecule: Actin Atom
MyosinActin
B. Organelle: Myofibril (found only in muscle cells)
Myofibril (organelle)
C. Cell and tissue: Muscle cell within muscle tissue
Rattlebox moth
D. Organ: Flight muscle of a moth
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A chemical _____ is a substance that cannot be broken down to other substances by ordinary chemical means
About ____ different chemical elements are essential to _____
lead
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Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life
_________ Table 2.2
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Goiters are caused by iodine deficiency
Figure 2.2
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The smallest particle of an element is an _____
Different ______ have different types of atoms
2.4 Atoms consist of protons, ________, and electrons
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An atom is made up of protons and neutrons located in a central nucleus
A. Helium atom
2
2
2
Protons
Neutrons
Electrons
Nucleus
The nucleus is surrounded by electrons
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Each atom is held together by attractions between the positively charged protons and ________charged electrons
B. Carbon atom
6
6
6
Protons
Neutrons
Electrons
Nucleus
Neutrons are electrically _______
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Atoms of each element are distinguished by a specific number of protons
– The number of neutrons may vary – Variant forms of an element are called
________– Some isotopes are ________
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Radioactive isotopes can be useful tracers for studying biological processes
PET scanners use radioactive isotopes to create anatomical images
2.5 Connection: Radioactive isotopes can help or harm us
Figure 2.5BFigure 2.5A
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Chemical elements combine in fixed ratios to form _________
Example: sodium + chlorine sodium chloride
2.3 Elements can combine to form compounds
Reactants Products
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Electrons are arranged in _______– The outermost shell determines the
chemical properties of an atom– In most atoms, a full outer shell holds
_____ electrons
2.6 Electron arrangement determines the chemical
properties of an atom
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Atoms whose shells are not full tend to interact with other atoms and ___, ____, or ______ electrons
Figure 2.6
HYDROGEN (H)Atomic number = 1
CARBON (C)Atomic number = 6
NITROGEN (N)Atomic number = 7
OXYGEN (O)Atomic number = 8
Electron
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
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When atoms gain or lose electrons, charged atoms called ions are created– An electrical attraction between ions with
opposite charges results in an ionic bond
2.7 Ionic bonds are attractions between ions of opposite charge
Figure 2.7A
NaSodium atom
ClChlorine atom
Na+
Sodium ionCl–
Chloride ion
Sodium chloride (NaCl)
Na Cl Na Cl
+–
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Some atoms share outer shell electrons with other atoms, forming covalent bonds– Atoms joined together by covalent bonds
form molecules
2.8 Covalent bonds, the _____ of electrons, join atoms into
molecules
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In a chemical reaction:– reactants interact– atoms rearrange– products result
Chemical reactions rearrange matter
REARRANGEMENTS OF ATOMS
2 H2+ O2
2 H2O
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A compound that releases H+ ions in solution is an acid, and one that accepts H+ ions in solution is a base
Acidity is measured on the pH scale: – 0-6 is acidic – 8-13 is basic OH- Hydroxide Ion Alkaline– Pure water and solutions that are neither
basic nor acidic are neutral, with a pH of 7
2.15 The chemistry of life is sensitive to acidic and basic
conditions
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The pH scale
pH scale
Acidic solution
Neutral solution
Basic solution
Incr
easi
ng
ly A
CID
IC(H
igh
er c
on
cen
trat
ion
of
H+)
Incr
easi
ng
ly B
AS
IC(L
ow
er
con
cen
trat
ion
of
H+)
NEUTRAL[H+] = [OH–]
Lemon juice; gastric juice
Grapefruit juice
Tomato juice
Urine
PURE WATER
Seawater
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
Human blood
H+
OH–
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Cells are kept close to pH 7 by buffers
Buffers are substances that resist pH change– They accept H+ ions when they are in
excess and donate H+ ions when they are depleted
– Buffers are not foolproof
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